Manufacture of cellulose ethers



Patented Apr. 28, 1953 NIANUFACTURE F CELLULOSE ETHERS Wiley MonroeBranan, Penns Grove, N. J., and v Lawton Arthur Burrows, Mendenhall, andBill Harry Mackcy, West Chester, Pa., assignors to E. I. du Pont deNemours & Company, Wilmington, DeL, a corporation of Delaware NoDrawing. Application April 27,1950, Serial No. 158,584

(Cl. 2fi0-231 8 Claims.

This invention relates to the manufacture of sodium carboxymethylcellulose and, more particularly. to an improved process for producing awater soluble sodium carboxymethyl cellulose.

This application is a continuation-in-part of our copen dingapplication, Serial No. 11,326, filed February 26, 1948, now abandoned.

The sodium salt of carboxymethyl cellulose is made by reacting cellulosewith an alkali and an etherifying agent such as monochloroacetic acid orsodium monochloroacetate. In general, two courses of action have beenopen for the production of water soluble sodium carboxymethyl cellulose.The first involves mixing the cellulose with the alkali and etherifyingagent in the presence of water as the only liquid. This is usuallyaccomplished by steeping the cellulose in an aqueous alkali solutionfollowed by pressing to remove the excess alkali. The alkali cellulosethus formed is shredded in a mixer equipped with serrated blades orsimilar equipment for a period of time suflicient to fluff or tear thematerial after which the etherifying agent is mixed in and reacted. Thisgeneral procedure is characterizcd by excessive times for mixing orintermingling of the ingredients to obtain uniform distribution of thereactants and to insure attainment of a reasonably uniform product.Moreover, substantially completely water soluble carboxymethyl cellulosecan be produced only by the adoption of excess ratios of the. reactingingredients. Thus it has been necessary to use excessive quantities ofexpensive monochloroacetic acid or sodium chloroacetate; Thedisadvantages from an. economic standpoint are obvious.

alternate method known in the art involves the addition of. an organicagent such as methanol, ethanol, isopropanol and the like to replace a.portion of the water otherwise required for distribution of the;ingredients. When such a course of action is pursued, the cellulose hasusually been in a shredded form resulting from passage of the cellulosethrough available commercial equipment which flufis or tears thecelluloss; but does. not destroy its fibrous characteristics. Suchshredded cellulose usually has a low bulk density of about 3 pounds percubic foot but may be as high as I2 pounds per cubic foot. When anorganic agent is used it is then possible to produce a water solublesodium carboxymethyl cellulose without employing excessive ratios of thereacting ingredient and with reasonable reaction efficiency. The organicmedium for which the cellulose has less affinity serves better todistribute the ingredients. Ex-

cluding part of the water which would otherwise be required to effectdistribution of the ingredients reduces the tendency of themonochloroacetic acid to hydrolyze to glycollic acid or its sodium saltand. thus effectively to be lost for etherifying purposes. The additionof an organic medium possesses disadvantages because of the expense ofthe medium itself as an essential material, because of the cost ofrecovering it and because all of the known organic agents which are usedin this process are flammable and form explosive mixtures with air sothat elaborate precautions must be taken to guard against accidentalexplosion.

The. object of the present invention. is an improved process forproducing a Water soluble sodium carboxymethyl cellulose- Another objectis a process characterized by high reaction efficiency which yields avfree-flowing, water soluble product of suitable degree: ofetherificatiom. A further object is. a process for making water solublesodium carboxymethyl cellulose which obviates; the needy for using anorganic medium. A still. further object is an. improved process. formaking water soluble sodium carboxymethyl eel.- lulose which ischaracterized by efficient utilization of reaction ingredients and whichis fur ther characterized by short periods for intermingling saidingredients.

We have found that, the: foregoing objects are obtained, by reacting apurified cellulose of granular form and having an average particle size:of less than 150 microns with an: alkali and an etherifying. agent suchas monochloroacetic acid or sodium chloroacetate. The term purifiedcellulose is intended to mean. what is known in the trade: as chemicalcellulose and is characterized by a. purity of. at least: 99% andhas' analpha contentof at least The term granular is used to distinguish. theform of cellulose particle from the usual fibrous form in which itocours or is available. The granules when examined: under a microscope:do not possess any of the usual fibrous characteristics. Furthermore,cellulose in this form: is free flowing and does nottend to mat as doesthe fibrous materia-l. The average bulk density of the granularcellulose is about 30 pounds per cubic foot.

We have found that purified cellulose in granular form as described inthe foregoing can bereacted with sodium hydroxide and monochloroaceticacid using ordinary mixing means in a short: period of time without thenecessity'of havingan organic mediumpresent to yield a water increase indegree of etherification and, in a uniformly substituted product,complete water solubility is considered to be obtained within a range ofdegree of etherification of at least 0.3 to 0.4. Furthermore, this canbe done without requiring excessive ratios of ingredients. Thus it ispossible to obtain the desired results by using a theoretical degree ofetherification (T. D. E.) between 0.7 and 1.3. Such actual degrees ofetherification at these theoretical degrees of etherification representreaction efficiencies in excess of The theoretical degree ofetherification is defined as the ratio of the mols of etherifying agentto the mols of cellulose and the reaction etficiency is defined as theratio of the actual degree of etherification to the theoretical degreeof etherification, multiplied by 100. The purity of the water solublecarboxymethyl cellulose resulting is on the order of to 75% on a drybasis. Solutions made with this material are characterized by theabsence of significant quantities of insoluble material.

The following examples will illustrate more specifically the modusoperandi of the present invention:

Example 1 173.5 pounds of a 36 percent aqueoussolution of sodiumhydroxide at 25 C. were placed in a 100 gallonWerner-Pfieiderer typemixer which was cooled by means of a brine solution at 14 C. circulatingthrough the mixer jacket. 150 pounds of the finely-divided granularcellulosic material (bulk density 30 pounds per cubic foot) were thenadded and the mixture agitated for 15 minutes. 34 /4 pounds ofmonochloroacetic acid were added and the mixing continued for 15minutes. 34 pounds of monochloroacetic acid were then added and themixing continued 30 minutes after which the mixture was removed andpermitted to react in a static state for 10 hours. The product was thenmilled to break apart the agglomeration and render it free flowing andthen packed. The product was essentially completely soluble in water.The sodium carboxymethyl cellulose content of the damp product was 48percent.- A sample which was dried completely had a sodium carboxymethylcellulose content of percent.

The formulation was based on a T. D. E. of 0.83. The actual degree ofetherification of the sodium carboxymethyl cellulose was 0.60representing a' reaction efiiciency of 72.3 percent.

Example 2 and permitted to react in a static state for 10 hours. Theproduct was returned to the mixer and 60 pounds of a 41.3 percentaqueous solution of orthophosphoric acid added and mixed 15 minutes. Theproduct was removed from the mixer, milled to break apart theagglomeration and to render it free flowing and then packed. The productwas essentially completely soluble in water. The sodium carboxymethylcellulose content of the damp product was 36.9 percent. The product maybe dried and milled to break apart the particle agglomerates and reduceit to the form of the original cellulosi-c ingredient. When driedcompletely,

the sodium carboxymethyl cellulose content of the product is 62 percent.

The formulation was based on a T. D. E. or 0.83. The degree ofetherification of the sodium carboxymethyl cellulose was 0.50representing a reaction efliciency of 60.2 percent.

Example 3 218 pounds of a 36.4 percent aqueous solution of sodiumhydroxide at 15 C. were placed in a 100 gallon Wcrner-Pfleiderer typemixer which was cooled by means of a brine solution at 14 C. circulatingthrough the mixer jacket. 150

pounds of the finely-divided granular cellulosic material (bulk density30 pounds per cubic foot) were added and the mixture agitated 10minutes. 34 pounds of monochloroacetic acid were added and the mixingcontinued 10 minutes. 34%; pounds of monochloroacetic acid were thenadded and the mixing continued 10 minutes after which the brine in themixer packet was exchanged for steam and the charge heated to C. It wasmaintained at 80 C. for 20 minutes additional mixing after which asolution of 60 pounds of 41.3 percent aqueous solution oforthophosphoric acid were added and mixing continued 15 minutes withcooling. The product was removed and milled to break apart theagglomeration and render it free flowing and then packed. The productwas essentially completely soluble in water and duplicated theproperties described for the product derived in Example 2. Theefiiciencies attributed to Example 2 were also dupli- .cated.

Example 4 217 pounds of a 36 percent aqueous solution of sodiumhydroxide at 15 C. were placed in a gallon Werner-Pileiderer type mixerwhich was cooled by means of a brine solution at -14 C. "circulatingthrough the mixer jacket. pounds of the finely-divided granularcellulosic material (bulk density 30 pounds per cubic foot) were thenadded and the mixture agitated for 15 minutes. 45 poundsofmon'dchloroacetic acid 'were added and the mixing continued for 15minutes. 45 /2 pounds of monochloroaceti-c acid were then added and themixing continued 30 minutes after which the mixture was removed andpermitted to react in a static state for 10 hours.

The product was then milled to break apart the agglomeration and renderit free flowing and then packed. The product was essentially completelysoluble in water. The sodium carboxymethyl cellulose content of the dampproduct was 42.8 percent. The product may be dried and milled whichbreaks apart the particle agglom crates and reduces it to the form ofthe original cellulosic ingredient. When dried completely, the sodiumcarboxymethyl cellulose content of the product is 67.1 percent.

, p The formulation was based on a T. D. E. of 1.10. The degree ofetherification otthe sodium carboxymethyl cellulose was 0.68representing a reaction efiiciency of 61.8 percent.

The foregoing examples represent several embodiments of the invention,said embodiments being directed to the production of technical grades ofthe sodium salt of carboxymethyl cellulose. These are referred to astechnical grades because the byproduct salts such as sodium chloride,sodium glycollate, and sodium phosphate (this latter salt being presentwhen the material is neutralized with phosphoric acid) have not beenremoved. In the event that it is desirable to obtain the sodium salt ofcarboxymethyl cellulose in a higher state of purity, the productsobtained above can be washed with various solutions of ethanol,methanol, and the like. The strength of the washing medium is selectedon the basis of having optimum solvent power for the removal or thesodium chlorides, glycollates and so forth without dissolution ofsignificant quantities of the sodium carboxymethyl cellulose. Thus, a65% by weight solution of ethanol has been established as suitable forthe purification treatment. Removal of the impurities is effected byseparation of the spent effluent from the solid by known methanicalmeans, viz. filters, centrifuges and the like. After washing, theresultant product may be dried in any suitable equipment normally usedfor the recovery of solvent vapors. The purity of the finished refinedproduct, of course, depends upon the efiiciency of the washingtreatment. Sodium carboxymethyl cellulose having a purity of about 99%has been prepared in this manner. Here again, the particle size of theproduct is similar to that of the granular cellulose employed as thestarting material.

In Examples I, II and IV, a very significant part of the reaction ispermitted to go on in the static condition, that is, after the materialhas been removed from the mixers. It is desirable, the temperatureduring mixing can be increased so that the reaction rate is increasedand essentially complete reaction can be obtained during the mixingperiod. This principle is illustrated in Example III. Need forpermitting the reaction to continue in the static condition afterdischarge from the mixers may thus be obviated.

Although monochloroacetic acid has been set forth as the etherifyingagent in the examples above, sodium chloroacetate can be used instead.

It will be understood that the examples given in the foregoing are setforth as specific embodiments of the invention and are not to beconstrued as limiting it. Thus acids other than phosphoric may be usedto neutralize the sodium carboxymethyl cellulose. Acetic acid, nitricacid, and hydrochloric acid have been used advantageously as theneutralizing agents, particularly where it is desired to purify thesodium carboxymethyl cellulose further. In general, acids-are selectedon the basis of the ease of removal of the salts they form by theparticular washing medium employed for the purification step.

We intend, therefore, to be bound only by the following claims.

1. A process for the production of water soluble sodium carboxymethylcellulose which comprises reacting purified cellulose granules having anaverage particle size of less than 150 microns with aqueous causticalkali solution and an etherifying agent, the ratio of the mols ofetherifying agent to the mols of cellulose being in the range of 0.7 to1.3, and water being the sole normally liquid ingredient present.

2. The process of claim 1, wherein the etherifying agent ismonochloroacetic acid.

3. The process of claim 1, wherein the etherifying agent is sodiumchloroacetate.

4. A process for the production of water soluble sodium carboxymethylcellulose having a degree of etherification of at least 0.4 whichcomprises reacting purified cellulose granules having an averageparticle size of less than microns with aqueous caustic alkali solutionand monochloroacetic acid, the ratio of the mols of etherifying agent tothe mols of cellulose being from 0.7 to 1.3, and water being the solenormally liquid ingredient present.

5. A process for the production of water soluble sodium carboxymethylcellulose having a degree of etherification between 0.40 and 0.75 whichconsists in mixing purified cellulose granules with an aqueous causticalkali solution, adding monochloroacetic acid in a ratio of the mols ofetherifying agent to the mols of cellulose range of from 0.7 to 1.3,intermingling said monochloroacetic acid with the alkali cellulose,permitting the resultant mixture to continue to react in a staticcondition and then milling it to yield a free flowing product.

6. A process for producing water soluble sodium carboxymethyl cellulosehaving a degree of etherification of at least 0.40, which comprisesintermingling purified cellulose granules with an aqueous causticsolution, adding to the resultant alkali cellulose monochloroacetic acidin such quantity that the ratio of the mols of etherifying agent to themols of cellulose is within the range of 0.7 to 1.3, permitting thereaction to go to substantial completion, and milling the resultantproduct, and water being the sole normally liquid ingredient present.

7. A process for producing water soluble technical grade sodiumcarboxymethyl cellulose having a degree of etherification between 0.4and 0.75, which comprises reacting purified granular cellulose with anaqueous sodium hydroxide solution, adding a quantity of monochloroaceticacid in the ratio of the mols of etherifying agent to the mole ofcellulose range of 0.7 to 1.3 to the resultant alkali cellulose, andwater being the sole normally liquid ingredient present, neutralizingthe resultant product containing sodium carboxymethyl cellulose havingan actual degree of etherification from 0.4 to 0.75, drying theneutralized material and milling to yield a granular free-flowingproduct.

8. The process of claim 7, wherein the neutralized material is purifiedby washing with an aqueous ethanol solution.

WILEY MONROE BRANAN. LAWTON ARTHUR BURROWS. BILL HARRY MACKEY.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,960,551 Richter May 29, 1934 2,060,056 Ellsworth Nov. 10,1936 2,067,946 Picton Jan. 19, 1937 2,236,545 Maxwell et al. Apr. 1,1941 2,278,612 Collings et al Apr. 7, 1942 2,294,666 Jahrstorfer et al.Sept. 1, 1942 2,332,048 Bock et al. Oct. 19, 1943 2,476,331 Swinehart etal. July 19, 1949 2,510,355 Waldeck Jun 6, 1950

1. A PROCESS FOR THE PRODUCTION OF WATER SOLUBLE SODIUM CARBOXYMETHYLCELLULOSE WHICH COMPRISES REACTING PURIFIED CELLULOSE GRANULES HAVING ANAVERAGE PARTICLE SIZE OF LESS THAN 150 MICRONS WITH AQUEOUS CAUSTICALKALI SOLUTION AND AN ETHERIFYING AGENT, THE RATIO OF THE MOLS OFETHERIFYING AGENT TO THE MOLS OF CELLULOSE BEING IN THE RANGE OF 0.7 TO1.3, AND WATER BEING THE SOLE NORMALLY LIQUID INGREDIENT PRESENT.